blocks|key|2505597|text|如果仅仅是关于日志记录，那么您可以|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2505598|fun+<T>+T?.logNull(name:+String)+{
++++when(this)+{
++++++++null+->+//log+'$name'+was+null
++++++++else+->+//do+nothing
++++}
}|code-block|syntax|javascript|2505599|并将其命名为|2505600|var+a:+String?+=+null
a.logNull("my+a+variable")+//+"'my+a+variable'+was+null"|2505601|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

If it is just about logging, you could:

<pre><code>fun &lt;T&gt; T?.logNull(name: String) {
 when(this) {
 null -&gt; //log '$name' was null
 else -&gt; //do nothing
 }
}
</code></pre>

and call it like

<pre><code>var a: String? = null
a.logNull("my a variable") // "'my a variable' was null"
</code></pre>

blocks|key|1671785|text|这肯定需要反射，因为你需要参数名。要使用下面的代码，您需要将反射添加为依赖项as+explained+in+the+documentation。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1671786|private+fun+listNullProperties+(vararg+props:+KProperty0<Any?>)+:+List<String>+{
++++val+list+=+mutableListOf<String>()
++++for+(prop+in+props)
++++++++if+(param.get()+==+null)
++++++++++++list.add(param.name)
++++return+list
}|code-block|syntax|javascript|1671787|用法：|1671788|val+nullPropertiesByName+=+listNullParameters(
++++::myProperty,
++++::myOtherProperty,
++++::myDateProperty
)
println(nullPropertiesByName.joinToString())|1671789|entityMap|0|LINK|mutability|MUTABLE|url|https://kotlinlang.org/docs/reference/using-gradle.html^0|12|X|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|Z|8|@]|9|@]|C|$]]|$1|K|3|L|5|F|7|10|8|@]|9|@]|C|$G|H]]|$1|M|3|-4|5|6|7|11|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]]]

This definitely requires reflection, since you want parameter names. You need to add reflection as a dependency <a href="https://kotlinlang.org/docs/reference/using-gradle.html" rel="nofollow noreferrer">as explained in the documentation</a> to use the below code.

<pre><code>private fun listNullProperties (vararg props: KProperty0&lt;Any?&gt;) : List&lt;String&gt; {
 val list = mutableListOf&lt;String&gt;()
 for (prop in props)
 if (param.get() == null)
 list.add(param.name)
 return list
}
</code></pre>

Usage:

<pre><code>val nullPropertiesByName = listNullParameters(
 ::myProperty,
 ::myOtherProperty,
 ::myDateProperty
)
println(nullPropertiesByName.joinToString())
</code></pre>

blocks|key|2505624|text|我仍然推荐Map-approach。您可能希望使用properties+stored+in+a+map来克服反射的使用。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2505625|下面是一个使用两个日期和两个字符串的类型的示例，这两个类型都有一个可以为空的变量和一个非空变量：|2505626|class+YourData(internal+val+backedMap+:+Map<String,+Any?>)+{
++val+beginDate+:+Date+by+backedMap
++val+endDate+:+Date?+by+backedMap
++val+maybeString+:+String?+by+backedMap
++val+string+:+String+by+backedMap
++constructor(beginDate+:+Date,+string+:+String,+endDate:+Date?+=+null,+maybeString+:+String?+=+null)+:+this(mapOf(
++++++"beginDate"+to+beginDate,
++++++"endDate"+to+endDate,
++++++"maybeString"+to+maybeString,
++++++"string"+to+string
++))
}|code-block|syntax|javascript|2505627|虽然有了这个额外的构造函数看起来更复杂，但它只是有助于以您最熟悉的方式轻松创建新对象。|2505628|现在，您可以提供我放在注释中的函数，也可以提供它的任何变体。我现在改用YourData的扩展函数：|2505629|fun+YourData.getKeysWithNullValues()+=+backedMap.filterValues+{+it+==+null+}.keys|2505630|用法可能如下所示：|2505631|YourData(Date(),+"test+string")
++.getKeysWithNullValues()
++.forEach(::println)|2505632|在本例中，它将打印：|2505633|endDate
maybeString|2505634|entityMap|0|LINK|mutability|MUTABLE|url|https://kotlinlang.org/docs/reference/delegated-properties.html#storing-properties-in-a-map^0|5|3|P|Q|0|0|0|0|0|Z|8|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|18|8|@$9|19|A|1A|B|C]]|D|@$9|1B|A|1C|1|1D]]|E|$]]|$1|F|3|G|5|6|7|1E|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|1F|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|1G|8|@]|D|@]|E|$]]|$1|O|3|P|5|6|7|1H|8|@$9|1I|A|1J|B|C]]|D|@]|E|$]]|$1|Q|3|R|5|J|7|1K|8|@]|D|@]|E|$K|L]]|$1|S|3|T|5|6|7|1L|8|@]|D|@]|E|$]]|$1|U|3|V|5|J|7|1M|8|@]|D|@]|E|$K|L]]|$1|W|3|X|5|6|7|1N|8|@]|D|@]|E|$]]|$1|Y|3|Z|5|J|7|1O|8|@]|D|@]|E|$K|L]]|$1|10|3|-4|5|6|7|1P|8|@]|D|@]|E|$]]]|11|$12|$5|13|14|15|E|$16|17]]]]

I still recommend the <code>Map</code>-approach. You may want to use <a href="https://kotlinlang.org/docs/reference/delegated-properties.html#storing-properties-in-a-map" rel="nofollow noreferrer">properties stored in a map</a> to overcome the use of reflection.

Here is an example using a type with 2 dates and 2 strings, both having a nullable and a non-null variant:

<pre><code>class YourData(internal val backedMap : Map&lt;String, Any?&gt;) {
 val beginDate : Date by backedMap
 val endDate : Date? by backedMap
 val maybeString : String? by backedMap
 val string : String by backedMap
 constructor(beginDate : Date, string : String, endDate: Date? = null, maybeString : String? = null) : this(mapOf(
 "beginDate" to beginDate,
 "endDate" to endDate,
 "maybeString" to maybeString,
 "string" to string
 ))
}
</code></pre>

While it may seem more complicated having that additional constructor in place, it just helps to easily create new objects the way you are most comfortable with.

Now you can either supply that function I placed in the comment or any variant of it. I now use an extension function for <code>YourData</code> instead:

<pre><code>fun YourData.getKeysWithNullValues() = backedMap.filterValues { it == null }.keys
</code></pre>

Usage then may look as follows:

<pre><code>YourData(Date(), "test string")
 .getKeysWithNullValues()
 .forEach(::println)
</code></pre>

which for this example would print:

<pre><code>endDate
maybeString
</code></pre>

I have multiple variables that can be nullable and i need to check them ( Strings and Dates ) .

I need a method where i pass it X number of variables and it returns me a list of the variables that are null.

I was thinking something that i can call like this : 

<pre><code>internal fun checkNullVariables ( var x, var y , ..... ) : MutableList&lt;String&gt;{

 // yada yada

 return listOfNamesOfNullVariables
}
</code></pre>

Kotlin multiple variables Null checker method implementation

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我有多个可以为空的变量，我需要检查它们(字符串和日期)。我需要一个方法，在这个方法中，我向它传递X个变量，它会返回一个变量列表，这些变量都是空的。我在想一个我可以这么叫的东西：internal fun checkNullVariables ( var x, var y , ..... ) : MutableList<S...

问Kotlin多变量Null检查器方法实现
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